This invention relates to an improved method and assembly apparatus for making a wooden beam fabricated from a pair of wood chord members and a web member interconnecting such chord members by means of glued or unglued joints.
The rising costs of sawn lumber in general and the scarcity of high quality wood capable of producing beams of large size have led to the development of processes for fabricating large beams from less expensive and more available wood products. The use of fabricated beams also permits more efficient design requiring less wood to provide a beam of given strength. This not only saves wood but also reduces the cost of transportation and facilitates the erection of wooden structures.
Where strength is required to support loads applied primarily in one direction, considerable saving of weight and material costs may be accomplished by using a fabricated wooden I-beam. This general design provides the required strength and support of compressive strength loads generated by application of a load to the top of the I-beam resting on supporting structure, as when such a beam is used as a rafter or joist.
When a downward load is applied to the top of an I-beam which has its ends supported from below and its "I" cross-section in an upright orientation, the stresses which are generated are generally distributed as compression along the top chord or flange portion of the I-beam and tension in the bottom chord or flange portion. The width of the top and bottom chords or flanges provides the required lateral stiffness allowing the use of a narrow vertical web connecting the flanges. Thus, for a given load supporting capacity in this type of environment, an I-beam is lighter than a solid beam having a rectangular cross-section.
This invention relates to methods and apparatus for making wooden I-beam structures wherein both the chord or flange members and the webs may either be solid wood members or composite or laminated wood members as desired. Beams of this general type have been disclosed extensively in the prior art as illustrated, by way of example, in U.S. Pat. Nos. 3,490,188, 4,074,498, 4,191,000, 4,195,462, 4,249,355, 4,336,678, 4,413,459, 4,456,497 and 4,458,465, the foregoing listing being intended as exemplary only and not as all inclusive.
Prior known procedures and arrangements for forming prefabricated wooden I-beams by gluing various members together have generally entailed the use of various sub-assemblies in which a series of webs are driven along a web conveyor line in either spaced or end-to-end abutting relationship, with a pair of grooved chords or flanges driven along opposite sides of the web conveyor. The flanges are driven with their grooves facing the webs and are gradually converged towards the conveyed webs so that the longitudinal web edges, often pre-glued, are forced to respectively enter the grooves to form an interconnecting glued joint therewith. Heat or radio frequency energy may be used to set the glue more quickly and the formed wooden I-beams emerging from the assembly line may then be cut, if necessary, to form a wooden I-beam of desired length.
Other sub-assemblies and mechancial procedures are employed to cut the chords or flange members to desired lengths and widths usually delivered to the I-beam production facility where a groove cutter is employed to cut a longitudinal groove along the length of the chord in one side thereof. Typically, however, wooden stock material of either random or constant lengths are delivered to the production facility where the material is split or cut substantially along the longitudinal axis to form a pair of chord members. These chord members are then conveyed to a separate sub-assembly containing a groove cutter for cutting the grooves as aforesaid. Other sub-assemblies are employed to cut the web members to desired length and width and thereafter to provide parallel beveled or shaped edges along longitudinal sides of the web members, such edges being generally complementary with the cross-sectional groove shapes.
In one prior art arrangement disclosed in Elford et al, U.S. Pat. No. 4,356,045, acquired by the assignee of the present application flanges or chord members pre-cut to desired width are joined together from random lengths to obtain corresponding top and bottom chords of desired length. Upon being cut, numerous sub-assemblies are then employed to groove the separate flange or chord members. These sub-assemblies include a chord transfer mechanism and production floor space therefor, a groove cutter staging area, a groove cutter conveyor, a groove cutter mechanism and an automatic repositioning mechanism for cutting a groove surface in the chord member one at a time.
The foregoing acts of cutting identical chords or flanges from wooden stock material of either random or standard length engenders the use of considerable handling of wooden material and corresponding machinery first to actually cut the material and then to actually deliver same to other machinery for groove cutting.
Separate equipment and operations are provided for longitudinal beveled or other shaped edges in the web members employed in prior known procedures and arrangements. In the above-identified Elford et al patent, for example, motor driven bevel forming heads are employed to create tapers on opposite longitudinal edges of the webs by introducing individual plywood web pieces, pre-cut to approximate width onto a web support drive roll which conveys the individual pieces past the straight cutting heads. The cutting heads are employed directly within the production line upstream from where the webs are successively conveyed into abutment with one another to form a continuous web material. In the event the bevel forming heads and associated drive and conveyor machinery require repair, a particular production run must be stopped until such repair is effected. In other words, there is no provision for stock-piling pre-cut, individual beveled web members for later use in a particular production run so that such production run is not dependent upon the act of beveling the individual web pieces during the actual run.
In the commercial practice of the Elford et al patent, a glue layer is applied to a leading transverse end of each web member as it is initially fed into the production line upstream from the bevel forming heads. As the pre-glued web members enter into contact with the bevel forming heads, glue from the leading end tends to drip down and enter between the bottom of the web member and an underlying bed plate or support on which the webs move past the bevel forming heads. This glue tends to form a film along which the bottom of the web members ride causing mis-alignment with the bevel forming heads which later result in an inferior joint with the interconnecting chords and the grooves therein.
Glue coated onto the leading transverse edge of each web prior to beveling is also to some extent absorbed into the porous wooden material forming the web. This occasionally results in inferior bonds between the webs when later moved into end-to-end relatiohship to form a continuous web, compromising the structural integrity of the formed wooden I-beam.
After the webs are joined to the length of each of a pair of chords forming the wooden I-beam, the beam is conveyed towards a cutting saw which is connected to a spring mounted feeler bar upstream from the saw that rides along one of the chords to sense the trailing end thereof. This trailing end is identified by driving preceding and succeeding respective top and bottom chords into joining contact with the web members to form a gap between the adjacent chords which is typically four to eight inches in length. The spring mounted feeler bar thus senses the trailing end by entering the gap. The web cutting saw is then pulled towards the gap to cut the web at the gap while moving at the same production line speed thereof. This gap must be trimmed from each adjoining free end of adjacent cut wooden I-beams resulting in wasted material and the requirement of trimming at least one end of each cut wooden I-beam following the cutting cycle.
According to other prior designs disclosed, for example, in Talbott, U.S. Pat. No. 3,477,485, Troutner, U.S. Pat. No. 3,616,091, Troutner et al, U.S. Pat. No. 3,894,908, individual flange groove cutters and web beveling heads are mounted directly within the associated production line. This means that additional machinery and handling was previously required to cut wooden stock material into substantially identical flange or chord members which are then fed into the production line for joining two webs.
Other arrangements and types of production line and related methods and apparatus for forming wooden I-beams have been proposed in the prior art, and it is to be understood that the foregoing discussion is intended as illustrative and not as all inclusive. While certain of these prior known arrangements and systems may provide one or more advantages, they also present problems and disadvantages.